As part of the process for utilizing nuclear fuel to generate power, the fuel is irradiated. The fuel can be, for example, UO2-based fuel, Mixed Oxide (MOX) fuels, and/or U-metal fuels. Irradiated nuclear fuel can be the product of the irradiation of many kinds of commercial fuels as well as defense fuels, and these fuels can be classified as spent fuel and/or irradiated uranium.
Processing this fuel, either before or after irradiation, can be problematic. Irradiated fuel can be particularly problematic in view of the various transmutated and fission products that are generated. Problems associated with the processing can include environmental and/or health hazards as well as problems associated with nuclear material safeguards and security, cost, storage, and/or disposal.
From an environmental and/or health standpoint for example, the fuel can contain components that have been classified as environmentally hazardous and/or toxic that must meet regulatory processing and disposition requirements. For example, certain actinide and fission products can dictate handling fuel according to comparably expensive methods rather than comparably inexpensive methods were such components below regulated levels. This handling can include highly regulated storage and/or disposal techniques. Also, previous processing techniques can introduce and/or generate environmentally hazardous components such as organic solvents and/or NOX, for example.
Further, the fuel contains valuable components whereby the recycling or extraction of such components is highly desirable. Uranium and/or plutonium within the fuel, for example, are valuable components that if recycled can provide for more cost efficient fuel and energy production as well as less waste for storage and/or disposal. In addition, the extraction of industrial- and medically-useful radioisotopes such as molybdenum-99 can be desirable.
In the past, these fuels have been treated according to what is referred to as the Plutonium and Uranium Extraction (PUREX) process. Generally, the fuel has been exposed to a hot nitric acid bath to isolate the uranium by oxidizing the UO2 to UO22+, for example. This process can dissolve the fuel matrix as well as all the fission products. While a great deal of energy is necessary to dissolve the fuel in hot nitric acid, aside from this additional energy expense, as the UO2 fuel is dissolved in the nitric acid, a large volume of NO and NO2 gases are formed and sent up processing stacks. Some noble gas fission products such as xenon and krypton can be completely released and proceed up the stacks as well. It has been found that fission products such as iodine and bromine also appear in the stack gases. Ruthenium also evaporates and can condense in the stacks. Tritium can be expelled up the stacks as well. Undissolved components of the hot nitric acid treatment can remain, and these components can include Mo, Tc, Ru, Rh, and Pd.
Following the nitric acid extraction, organic extractants such as tributyl phosphate (TBP) are dissolved in organic solvents and used to facilitate the separation of the actinides from each other and from other fission products. Problematically, these processing techniques accumulate combustible organic solvents and corrosive acids which can result in radiation induced solvent degradation. Further, valuable actinides may be lost among fission product waste and highly radiotoxic mixed wastes may be generated.